More optimal byte reversing

mtproto/wrappers/crypt.go

 }
 
 func reverseBytes(data []byte) []byte {
-	rv := make([]byte, len(data))
-	for k, v := range data {
-		rv[len(data)-1-k] = v
+	dataLen := len(data)
+	rv := make([]byte, dataLen)
+
+	rv[dataLen/2] = data[dataLen/2]
+	for i := dataLen/2 - 1; i >= 0; i-- {
+		opp := dataLen - i - 1
+		rv[i], rv[opp] = data[opp], data[i]
 	}
 
 	return rv